Current trends in lighting for automobile vehicles are strictly tied to aerodynamic and aesthetic requirements. Thus, modern automobile vehicles comprise a plunging bonnet line and a frontal area of reduced height. It is therefore necessary to correspondingly reduce the height of the vehicle headlamps.
A well known solution to this problem consists of using a headlamp which is conventional in optical design and comprises a lamp the filament (or other light source) of which is focussed in a parabolic reflector, and to truncate the reflector with two flat upper and lower reflecting surfaces.
This solution, although simple, has however a major disadvantage. Since the filament is usually horizontal (axial or transverse), it emits a large amount of the flux towards these surfaces which are inoperative optically and do not cause it to participate in the road beam obtained. In practice the flux recovery in such a lamp rarely exceeds 65%.
Attempts have been made, particularly by the applicant, to improve the flux recovery in such a truncated reflector. For example, the use of complex surfaces for the reflector to decrease the mean focal distance and enable a reflector to be obtained which is deeper, thus giving a better recovery of flux. The results obtained however still leave a margin for improvement.
It is one object of the present invention to reduce the disadvantages of the prior art and to provide a lamp capable of emitting a road beam which, whilst having a greatly reduced height to satisfy the most modern design requirements, produces a light beam of great intensity resulting from a good recovery of the flux emitted by the light source.
Another object of the invention is to give the images of the filament formed by the reflector an orientation which is particularly adapted to the formation of a road beam. In this connection it should be remembered that the visual comfort of a road beam is given, on the one hand, by a point of concentration on the axis of the road (that is to say the optical axis of the lamp) and, on the other hand, by a large width and small depth of the beam.
A further object of the invention is to provide that a large proportion of the images of the filament participating in the formation of the beam are horizontal or slightly inclined.